In laser receivers used for ranging it is necessary to provide an operating bias to a photo-detector which receives the target reflected laser signal as an input and provides an electrical signal as an output to a preamplifier in the receiver system. The prior art has used two basic techniques to provide such bias to a photo-avalanche diode. One technique has used temperature compensation to adjust the bias voltage responsively to prevailing ambient temperature level. A second technique has used noise regulation. Temperature compensation biases the diode as a function of ambient temperatures. The variations between individual diodes result in partial matching and hence degraded performance. Hence it is necessary to adjust the biasing level sufficiently below the avalanche breakdown point to allow for variations in the characteristics of individual diodes used as parts of different receivers.
Noise regulation is utilized in receivers which automatically track the diode noise and compensate for variations in the characteristics of the particular diodes used as a part in a particular receiver. However, the noise at cold temperature is not sufficient to operate this system and artificial optical noise is therefore required. This noise tracking technique is complex and utilizes time division or frequency division multiplex systems of preamplifiers and threshold circuits to achieve the regulation. The system also requires several seconds for stabilization.